1. Field of the Invention
The present invention relates to a dichroic prism, and more particularly to a dichroic prism suitable for use in an image projection apparatus that offers a high output of light.
2. Description of Related Art
In recent years, research and development have been done on projectors (image projection apparatuses) that project image data in the form of digital data by the use of a micro display device (image display device) such as a reflective liquid crystal panel or a DMD (digital micromirror device). A number of such projectors have already been put into practical use. Such projector can project high-quality images with natural colors without image deterioration, and thus have recently come to be used in movie theaters and the like in place of conventional projectors that project images distributed on film. A projector that projects images onto a large screen in a movie theater or the like is required to offer a very high output of light of 15 000 lumens or more.
Inconveniently, however, when conventional projectors are kept being used at such high outputs, the projected images gradually deteriorate. Such deterioration of projected images is particularly notable in projectors that employ a DMD, which reflects in different directions image light, that is, light for projecting images, and unnecessary light.